Thymic Carcinoma With Malignant Effusion—a Rare Cytologic and Radiologic Mimicker of Metastatic NSCLC

The predominant differentials for malignant pleural effusion are metastatic lung and breast carcinomas and mesothelioma 1 Poon I.K. Chan R.C.K. Choi J.S.H. et al. A comparative study of diagnostic accuracy in 3026 pleural biopsies and matched pleural effusion cytology with clinical correlation. Cancer Med. 2023; 12: 1471-1481https://doi.org/10.1002/cam4.5038 Crossref Scopus (4) Google Scholar ; hence, a limited panel of immunocytochemistry with heavy reliance on TTF-1 is often used. 2 Li J.J.X. Ng J.K.M. Aphivatanasiri C. et al. Fine needle aspiration cytology of metastatic carcinomas with papillary architecture: a systemic assessment of clinical, cytological and immunohistochemical parameters. Cytopathology. 2022; 33: 328-343 Crossref Scopus (4) Google Scholar Here, we describe a rare case of malignant effusion owing to thymic carcinoma with TTF-1 positivity, initially considered as metastatic NSCLC on effusion cytology.